In this type of damper disc, two torsion springs are disposed in series in an opening in order to assure wide twisting ranges, and an intervening support plate is inserted between torsion springs in a manner free to move in the circumferential direction.
The present applicant developed and applied a structure, in such damper disc of spring series type, of coupling support plates 51 to annular coupling plates 52 with pins 53 as shown in FIG. 4, in order to prevent the support plates from thrusting out in the radial direction by centrifugal force (unopened Japanese Utility Model Applications 63-38836, 63-84777).
However, the support plates 51 are disposed in a plane vertical to the clutch axial center, and an intermediate member (float element) 55 made of resin is pinched by a pair of support plates 51 spaced in the axial direction, and the springs 18 are received by their ends in the rotating direction.
That is, the spring 18 is received by the end which has a very small contacting area, and the surface pressure rises, which required improvements from the viewpoint of durability. Still worse, since the spring 18 does not receive the entire end surface in the rotating direction, the spring 18 may get loose during operation and tend to be unstable. Besides, since the pin 53 for oscillatably supporting the support plate 51 is positioned at a point enclosed by front and rear springs 18, and the support plate 51 is positioned at right angle to the clutch axial center, the limit of the setting length of the spring 18 in the rotating direction becomes large, and the degree of freedom for setting the torsional characteristic is limited.